1. Field of the Invention
This invention generally relates to a disk enclosure for containing a plurality of disk apparatuses which constitute a RAID (Redundant Array Inexpensive Disks) apparatus and so on, and particularly to a disk enclosure which can detect excessive current appropriately for each of the contained disk apparatuses.
2. Description of the Related Art
A disk enclosure referred to as a device enclosure (DE) contains a plurality of disk apparatuses, has a function of supplying electric power to these disk apparatuses, and a HUB function for data interfaces. In a disk enclosure of this type, a current detection and control circuit is inserted between each of the disk apparatuses and a power source at the back panel. There are following two objects for which the current detection and control circuit is inserted.
One object is to enable insertion and removal of the disk apparatus with the disk enclosure which is activated by supplying of the power. The other object is to limit the range of an effect, in a case that a power fault (for example, excessive current due to a short circuit of a capacitor) is caused in one of the disk apparatuses. Examples of power faults actually occurred is such faults an excessive current protection circuit is activated at the power unit, thereby a power supply is cut off for whole of the disk enclosure.
FIG. 5 is a block diagram illustrating an example of the excessive current protection circuit of a conventional disk enclosure. In FIG. 5, reference numeral 1 denotes a power supply unit, reference numeral 2 denotes a back panel unit of a disk enclosure, and reference numeral 3 denotes a disk apparatus unit in which disk apparatuses are contained.
When a disk apparatus is inserted and connected to a connector 22, a power source 10 supplies the disk apparatus with electric power, through a connector 11, a current detection element (resistor) 200, a transistor (FET) 21, and the connector 22. In the normal condition, a current control circuit 24 keeps an FET 21 turned on. A voltage detection circuit 23 detects potential difference between both terminals of the detection element 200. Based on the potential difference detected by the voltage detection circuit 23, the current control circuit 24 determines whether or not the current which flows into the disk apparatus is within a predetermined design value of current carrying capacity (designed tolerance value). When the current control circuit 24 detects a current exceeding the designed tolerance value, the current control circuit 24 turns the FET 21 off to cut off the current flowing into the disk apparatus unit 3, thereby protecting a disk apparatus internal circuit 30 and so on.
Japanese Patent Laid-Open No.3-280261 and Japanese Patent Laid-Open No. 2005-73340 disclose other conventional techniques to detect an excessive current or to control a current which flows into a magnetic disk apparatus. However, these conventional techniques are to control the current which flows into single magnetic disk apparatus in which a design value of its consumption current is fixed, and do not have their objects, in a disk enclosure containing a plurality of disk apparatuses, to detect a current which flows from a common power source unit to each of the disk apparatuses, and to protect each of the disk apparatuses from the excessive current.
In a disk enclosure such as a RAID apparatus and so on, a current detection and control circuit detects whether or not a value of the current supplied from a common power source unit to each of the disk apparatuses is within a normal range respectively. In this detection, the respective values of the consumption current are different from every type of the disk apparatuses. A value of a resistor for current detection has to be made to fit to a type of the disk apparatus which has a maximum consumption current among the disk apparatuses to be used. This will cause some problems as follow.
First, in a case that the resistance value of the resistor for current detection is made to fit to a type of a disk apparatus which has the maximum consumption current, it can be detected such a fault mode without any problem that flows an excessive current caused by a short circuit between a power source and the ground with regard to a disk apparatus which has a small consumption current (tentatively referred to as a disk A). However, when a fault mode occurs in which a current that is excessively larger than the consumption current of the disk A flows, even the excessive consumption current may smaller than the design value. Therefore, the fault mode can not be detected.
Moreover, it is assumed that a consumption current of a newly developed disk apparatus will increase excessively which has not been commercialized at this moment. In this case, the disk enclosure cannot deal with the new disk apparatus.